The recovery of large quantities of energy present in large flow volumes of industrial flue gases laden with abrasive dust and fines, including gases from blast furnaces, coal gasification and petroleum refining equipment such as fluid catalytic cracking devices, present unresolved and challenging problems for energy conservation engineers. In these and the like operations, hot pressurized gases must be wasted to the atmosphere on a continuous uninterrupted basis. Heretofore attempts to recover major portions of this energy have been unsuccessful owing to the fact that no satisfactory provision has been available for diverting the gas flow from recovery equipment to permit servicing operations without interrupting the operation of the continuous source of hot gases.
For example, a typical high volume source of hot gases comprises the waste gas output of a fluid catalytic cracking unit employed in a petroleum refining system. Typically, 150,000 actual cubic feet per minute of these flue gases are discharged at a pressure ranging between 30 and 40 psig, a temperature of 1,000.degree. to 1,350.degree. F. and are laden with abrasive contaminants including erosion producing particulates, and 5% to 10% of combustible carbon monoxide gas. The high energy content of such gases is readily recoverable in well known energy generating equipment such as a steam boiler, often called a CO boiler, rotary gas expanders and the like. However, such generators require deactivation and servicing at intervals but prior to this invention, it has not been practical to isolate them without shutting down the process unit for periods of up to ten days at an average loss of production amounting to hundreds of thousands of dollars and necessitating deactivating and reactivating all equipment associated with the production of the flue gases.
Various proposals have been made for a cut-off valve for the hot gas intake to the power recovery components having a valve element and a cooperating seat capable of withstanding long exposure to extremely hostile conditions in the flow ducts and thereafter reliably cutting off the flow when there is need for servicing operations. Such prior proposals include valves of the type disclosed in the following U.S. Pat. Nos. Kinney et al 3,105,672; Bowman et al 3,532,321; Pease 3,620,242; Yamamoto 3,946,752; Raftis 3,749,115; Adams 4,003,394; Kitner 3,032,108 and Herr 4,077,432.
Each of these prior proposals is subject to serious shortcomings and is unreliable and unsatisfactory for energy conservation applications of the type herein contemplated. Some propose elastomeric sealing components between the valve member and the duct wall manifestly incapable of providing a seal under the pressure and temperature conditions typical of hot pressurized flue gases. Others propose a rotary plate valve disc designed to close against the duct wall when inclined acutely to a diametric plane through the duct and relying upon movably supported sealing components at the periphery of the disc to accommodate variation in construction tolerances, expansion of components, erosion of valve parts etc. In some instances the movable parts are flexible and in others the parts are shiftable in the plane of the valve member; all require fasteners in the assembly operation.
Operation of such valves is highly unreliable and undependable for various reasons. For example, fasteners are notoriously failure-prone owing to the prevailing high operating temperatures and the extremely severe erosion caused by the particulate laden gases. The heads of the fasteners frequently pop off and, if they do not, they are subject to rupture and shear failure when attempts are made to disassemble them for servicing. Certain designs employ pressurized gases supplied to the valve seat at a pressure adequate to block escape of the hot particulate laden gases past the valve when closed, the pressurizing gas being supplied through the tubular valve shaft. Such tubular shafts are objectionably large in diameter thereby seriously interfering with the flow of gases when the valve is open and have inadequate strength when the valve is closed. Some constructions endeavour to minimise these shortcomings by rifle-boring the shaft to permit use of a smaller diameter shaft but this is a costly design and necessitates a higher pressure supply of the valve sealing gas. Still other proposals provide a pair of rectangular valves disposed side-by-side crosswise of a rectangular duct. Such a non-circular duct is highly undesirable under the high pressure, high temperature operating conditions typically present in energy recovery operations. Furthermore, a square or a rectangular valve inherently posesses very poor and inefficient seal properties along its lateral radial edges.